This species is characterized by developed stems with generally opposite leaves that sometimes have fascicles of axillary leaves and/or spinescent short-shoots, medium-sized leaf blades, paniculiform inflorescences, small 5-merous flowers with funnelform corollas, and obovoid fruits that are densely strigillose. Machaonia acuminata is similar to Machaonia martinicensis, which is much less commonly collected.
The name Machaonia acuminata has long been used for this species (Lorence et al., 2012), and these plants appear to match its type. However, the type collection by Bonpland is the apparently only specimen documenting this species from northwestern South America. Lorence et al. (2012) reported this species from Colombia, but specimens included in Machaonia acuminata that have been seen in this study have been re-identified as Machaonia martinicensis. Plants from inland Venezuela that were included by Steyermark in Machaonia brasiliensis also seem to match the Bonpland's type, however, and there are other instances known of incorrect locality attribution for his specimens. The name Machaonia acuminata is here used for the Central American and Mexican plants following previous authors, but the taxonomy of these and the Venezuelan species deserves further study.
The name Machaonia acuminata has been applied also to plants of eastern and southeastern Brazil (e.g., Schumann, 1889) or to all of the South American plants of Machaonia (e.g., Bernardi, 1985; Delprete, 2019). These plants are, like many species of Machaonia, all generally similar morphologically. However, biogeographically and morphologically these are distinct, and Machaonia acuminata is includes only plants from the biogeographic Central American region. Bacigalupo (1957) studied this group in some detail and Steyermark (1974) later reviewed it again, and they both concluded that Machaonia acuminata is not present in southern South America and their taxonomy is followed here.